There could be a problem with 2 players:You cannot deliver your goods to your own towns, so you are depending on the builds of the one other player to ship your goods. You could easily stalemate the game by refusing to build the last town(s) the other player needs to ship goods. It is also possible to block the other player's direct route of access to your towns by building incomplete routes. This could make them spend much more resources going around you. Lowering the amount of goods may resolve this problem satisfactorily.

It is better as a 3-4 player game, because there are more people looking out for their own interests, which ultimately means more places for you to ship your goods.

A 2 player version seems to be possible and a 5-6 player version seems to be possible (with additional components) as long as the number of towns and goods is adjusted. Keep in mind, there are only so many initial places to build and total places to build.

Recommendations for playtesting(In addition to first 3 towns placed on the board during setup):

I think the big holdup on 2 players would be the spots you can deliver goods to. Particularly since any "neutral" spots would end up on the eastern side of the board. Also, it would deplete the east coast a lot slower since only two of you are moving westward.

so how about a variation of building other-color cities that you can deliver to?

Then I start thinking that wants more grain and cattle than a whole other player who would be wanting ore and coal, too, so...

How about this?- Each player plays one color of their own. Also, set up a secondary color for each player, but with only 6 cities, 6 locked goods cubes, 1 starting goods cube, 1 settler, and 1 train.- The secondary-color settler is built as normal, moves as normal, and produces cities of that color (creating a new spot to deliver to).- The secondary-color train is built as normal and moves as normal, but requires paying 1 gold to the bank for right-of-way on your primary-color rails, which also means it needs a 1 gold payment when it is built on your rail. It can deliver goods of its matching color to your own cities at a cost of 1 gold per delivery. (Thus it can reduce the number of spots the opponent can deliver to.)